Axle nut drilling frustrations-learn from my mistakes

Gents,

I am completing the drilling process on my RV-7A gear and I am rather frustrated.

I followed the directions to drill the axle nut and wasn't pleased with the outcome.

Here is what I did.

I installed the wheel and tightened the nut the appropriate amount. I used a transfer punch in the 1/8" holes in the nut to mark the axle. I ran a #40 long drill to cut a little of the thread so that the nut could be easily removed. I then removed the nut and wheel. The nut came off with some resistance and small aluminum thread shaving were removed in the process. I used my drill press to drill each side on the axle for the cotter pin hole.

When I installed the wheel and nut I had a misalignment with one of the holes in the axel. Slightly off in rotation and off along the axle axis. This was caused by the fact that drilling holes in treads isn?t exact. So to fix this problem I decided to use a small round file and slot the hole in the axel. After filing for a while I was able to finally get the cotter pin in. It definitely fought me all the way.

I know where I made my mistake so I decided to try another approach on the other gear leg. This time I only marked one side with the transfer punch and drill, removed the wheel/nut (I needed to use a large wrench to get the nut off-deformed threads) and drilled only one side with the drill press. Then I installed the nut and inserted a 1/8 rivet into the nut/hole to pin the nut in position on the axle. I went back to the drill press and using the nut hole as a guide drilled the remaining hole in the axle. This method worked well except the original hole shifted slightly along the axle axis and when the nut is tightened down the holes don't align as they should. When they do align I do not get the preload I had intended. So I have too much slop (not enough preload) when the nut is installed and the cotter pin is in place.

This has been a frustrating day.

I am considering drilling a second cotter pin hole in the first gear leg using the method I used on the second gear leg but I hate to have extra hole in my project. As far as not having enough preload, I can do a few things. First I can make a new axle spacer that is wider then the supplied unit or purchase axle shims or I can order a new nut and maybe it will work well.

If after drilling the holes the nut can not be tightened down enough to get the holes aligned there is a rather easy fix for that. Just sand down the face of the nut until the holes align (material removal). If on the other hand you need to add material (that is my case) the solution is a little more involved.

It sure would be nice to have slots in the nuts instead of holes (future business opportunity?) sort of like a castle nut. That would make things much easier.

I wanted some input (opinions) on the next steps.

Thanks,

Paul

RV-7A (Finishing Kit)

I had the same problem Paul and I'm anxiously awaiting some solutions from your post. There has to be a better way. I'll better the guys building Cessnas don't wait until they put the wheels on before they drill the axles. It looks like Vans could drill the axle and have 2 or 3 holes in the nuts then include some spacers for fine adjustment.

Danny

You could ream the holes out to a slightly larger diameter. That'll make it easier to get the cotter pin in if there's a slight misalignment.

Drilling Axle RV-7A - Easy Done Deal

This is the way I've always done it... Assemble as per plans using the front wheel axle nut. The front axle nuts are slotted, or at least the one I have is. Set your pre-load. Make sure and set it two the three times for an extra check. Mark the axle at the edge of the nut with a sharpie (no not with Dan-C ;-)... Remove the assembly. Measure the drill spot in the main gear axle nut and screw on the temporary nut from the front axle backwards. Then screw the main gear nut on and add the difference past the (sharpie) mark to the drilled hole in the main gear nut. Lock it down the front gear nut to the main gear nut tight. Drill a hole that fits the slot and remove all nuts. Ream and you're done. Worked for me!

JMHO


Darrell

easier yet

Didn't want to post a solution until I had a chance to give it a try on my RV-3 today. Worked great, so I'll pass it along. Position the nut, then use a 12" #30 drill in the hole of choice. Drill just enough to make a mark. Remove the nut and wheel, then use a cutoff wheel to flatten the area around the mark, removing all the threads in a 1/4" dia circle around the mark. Reassemble, drill enough of a hole to center a drill, then remove the nut and wheel. Use a 1/8 cobalt drill to complete the hole. Do the opposite side with the wheel off the axle.

Tony

Drilling axles for cotter key

Tony Spicer said:

Didn't want to post a solution until I had a chance to give it a try on my RV-3 today. Worked great, so I'll pass it along. Position the nut, then use a 12" #30 drill in the hole of choice. Drill just enough to make a mark. Remove the nut and wheel, then use a cutoff wheel to flatten the area around the mark, removing all the threads in a 1/4" dia circle around the mark. Reassemble, drill enough of a hole to center a drill, then remove the nut and wheel. Use a 1/8 cobalt drill to complete the hole. Do the opposite side with the wheel off the axle.

Tony

Click to expand...

Tony had the best procedure I could find on VAF. Only addition I might add is to reference the Timken website on the subject of preload of bearings. The gist of it, is that "some" preload is preferred. They were a bit fuzzy on what "some" means, but this was our solution. A fairly large amount of torque was put on the nut while spinning the wheel, backed off and repeated 3-4 times to seat the bearings. Then prior to drilling, the nut was tightened only as much as could be done by hand. Pre-drilling torque on the nut was pretty high since it is easier to drop the preload by sanding the spacers a bit, rather than to shim a too loose wheel to get the preload back up. After drilling one hole with a 12" long #30 bit, I removed the wheel/tire, reinstalled the nut and pinned it in place thru the drilled hole with a #30 rivet, before drilling the opposite side hole. A little deburring with a countersink left a beautiful hole that looks factory done. Reinstall and pinning of the wheel nut, gave a wheel spin of about 4 rotations, which sounds on par with other posts. Tony's idea of flatting the threads a bit (in our case with a small Dremel rotary file) worked great, so that the drill bit would cut a clean hole and not wander around before drilling thru the axle.
Here's the link to Timken pdf on bearing preload:

http://www.timken.com/products/bearings/techtips/PDFs/Vol6No3.pdf

One other thought is to stamp the axle nuts as "L" or "R" since they are now custom fit to their respective sides.

Dave Milliken
RV-7QB Slider
Layton, Utah
Current Status: WIP: firewall forward & electrical routing

I just drilled my axles and my nose gear strut using the "Spicer Method" (see above) I highly recommend it. I used a small sphere shaped rotary burr on a Dremel tool to flatten the threads before I located and drilled the final hole instead of a cutoff tool. It worked great. Thanks for the tip Tony.

Tony Spicer said:

Didn't want to post a solution until I had a chance to give it a try on my RV-3 today. Worked great, so I'll pass it along. Position the nut, then use a 12" #30 drill in the hole of choice. Drill just enough to make a mark. Remove the nut and wheel, then use a cutoff wheel to flatten the area around the mark, removing all the threads in a 1/4" dia circle around the mark. Reassemble, drill enough of a hole to center a drill, then remove the nut and wheel. Use a 1/8 cobalt drill to complete the hole. Do the opposite side with the wheel off the axle.

Tony

Click to expand...

I used Tony's method too. Didn't have to grind any threads away though and didn't get many if any aluminum burrs. Guess I was lucky. Used a #30 drill bit to pin nut in place before marking and drilling opposite side of nut in a similar way.

Jim Sharkey
RV6

Question?

I am not to this point yet and don't have my finishing kit.

Does Vans supply a nut like this...

http://www.gen-aircraft-hardware.com/images/pdf/ms21025.pdf

Or is it something non-standard for an axle nut?

For the nose gear.

21025-20 is what secures the fork to the nose gear on the -7A. The main gear uses a different, aluminum nut which has a flat surface for a platenut that holds the wheel pant. This is shown (sort of) on DWG C-2.

Thanks.

rvtach said:

21025-20 is what secures the fork to the nose gear on the -7A. The main gear uses a different, aluminum nut which has a flat surface for a platenut that holds the wheel pant. This is shown (sort of) on DWG C-2.

Click to expand...

It's my turn to appreciate your tech support.

Thanks Jim.

I am a long time from doing this yet but somewhere in the back of my mind I remember that to set the preload on this type of wheel bearing what you do is torque the nut to 25 ft lbs while turning the wheel and then back it of to 5 ft lbs. my advice is worth what you pay for it.